Electromechanical coupling factors of single-domain 0.67Pb (Mg _1/3Nb_2/3)O₃-0.33 PbTiO₃ single-crystal thin films

Thin films of single c -domain/single-crystal (1-x)Pb (Mg_1/3 Nb_2/3)O₃-x PbTiO₃ (PMN-PT) with x≃0.33 near a morphotropic boundary composition were heteroepitaxially grown on (110)SRO/(001)Pt/(001)MgO substrates. The heteroepitaxial growth was achieved by rf-magnetron sputtering at the substrate temperature of 600 °C. After the sputtering deposition, the substrates were rapidly cooled from 600 °C to room temperature by atmospheric air gas at a cooling rate of 100 °C/min. The rapid cooling process enhanced the heteroepitaxial growth of the single c -domain/single crystal PMN-PT thin films. Their electromechanical coupling factor k_t measured by a resonance spectrum method was 45% at resonant frequency of 1.3 GHz with phase velocity of 5500 to 6000 ms for the film thickness of 2.3 μm. The d₃₃ and d₃₁ were 194 pCN and -104 pCN, respectively. The observed kd_t, d₃₃, and d ₃₁ were almost the same to the bulk single-crystal values. The present PMN-PT thin films are applicable for a fabrication of GHz planar bulk acoustic wave transducers.